Schizophrenia is a chronic and debilitating psychiatric disorder affecting approximately 0.45-1% of the world's population (van Os, J.; Kapur, S. “Schizophrenia” Lancet 2009, 374, 635-645). The principal goals of treatment are to achieve sustained remission from psychotic symptoms, reduce the risk and consequences of relapse, and improve patient functioning and overall quality of life. While many patients with schizophrenia are able to achieve symptom stability with the available antipsychotic medications, poor adherence to medication is a common reason for relapse with daily administered oral medications. Several studies (Abdel-Baki, A.; Ouellet-Plamondon, C.; Malla, A. “Pharmacotherapy Challenges in Patients with First-Episode Psychosis” Journal of Affective Disorders 2012, 138, S3-S14) investigating the outcomes of non-compliance have shown that patients with schizophrenia who do not take their medication as prescribed have higher rates of relapse, hospital admission and suicide as well as increased mortality. It is estimated that 40 to 75% of patients with schizophrenia have difficulty adhering to a daily oral treatment regimen (Lieberman, J. A.; Stroup, T. S.; McEvoy, J. P.; Swartz, M. S.; Rosenheck, R. A.; Perkins, D. O.; Keefe, R. S. E.; Davis, S. M.; Davis, C. E.; Lebowitz, B. D.; Severe, J.; Hsiao, J. K. “Effectiveness of Antipyschotic Drugs in Patients with Chronic Schizophrenia” New England Journal of Medicine 2005, 353(12), 1209-1223).
Therapeutic drug monitoring (TDM) is the quantification of serum or plasma concentrations of drugs, including anti-psychotic drugs, for treatment monitoring and optimization. Such monitoring permits, for example, the identification of patients that are not adhering to their medication regimen, that are not achieving therapeutic doses, that are non-responsive at therapeutic doses, that have suboptimal tolerability, that have pharmacokinetic drug-drug interactions, or that have abnormal metabolism resulting in inappropriate plasma concentrations. Considerable individual variability exists in the patient's ability to absorb, distribute, metabolize, and excrete anti-psychotic drugs. Such differences can be caused by concurrent disease, age, concomitant medication or genetic peculiarities. Different drug formulations can also influence the metabolism of anti-psychotic drugs. TDM permits dose optimization for individual patients, improving therapeutic and functional outcomes. TDM further permits a prescribing clinician to ensure compliance with prescribed dosages and achievement of effective serum concentrations.
To date, methods for determining the levels of serum or plasma concentrations of anti-psychotic drugs involve the use of liquid chromatography (LC) with UV or mass spectrometry detection, and radioimmunoassays (see, for example, Woestenborghs et al., 1990 “On the selectivity of some recently developed RIA's” in Methodological Surveys in Biochemistry and Analysis 20:241-246. Analysis of Drugs and Metabolites, Including Anti-infective Agents; Heykants et al., 1994 “The Pharmacokinetics of Risperidone in Humans: A Summary”, J Clin Psychiatry 55/5, suppl:13-17; Huang et al., 1993 “Pharmacokinetics of the novel anti-psychotic agent risperidone and the prolactin response in healthy subjects”, Clin Pharmacol Ther 54:257-268). Radioimmunoassays detect one or both of risperidone and paliperidone. Salamone et al. in U.S. Pat. No. 8,088,594 disclose a competitive immunoassay for risperidone using antibodies that detect both risperidone and paliperidone but not pharmacologically inactive metabolites. The antibodies used in the competitive immunoassay are developed against a particular immunogen. ID Labs Inc. (London, Ontario, Canada) markets an ELISA for olanzapine, another anti-psychotic drug, which also utilizes a competitive format. The Instructions For Use indicate that the assay is designed for screening purposes and intended for forensic or research use, and is specifically not intended for therapeutic use. The Instructions recommend that all positive samples should be confirmed with gas chromatography/mass spectrometry (GC-MS), and indicate that the antibody used detects olanzapine and clozapine (see ID Labs Inc., “Instructions For Use Data Sheet IDEL-F083”, Rev. Date Aug. 8, 2011). Some of these methods, namely HPLC and GC/MS, can be expensive and labor-intensive, and are generally only performed in large or specialty labs having the appropriate equipment.
A need exists for other methods for determining the levels of anti-psychotic drugs, particularly methods that can be performed in a prescribing clinician's office (where the treatment for an individual patient can be adjusted accordingly in a much more timely manner) and in other medical settings lacking LC or GC/MS equipment or requiring rapid test results.